Australian Bockadam

description

Description of Holotype. A female, 687 mm SVL, 126 mm tail (tail incomplete). Head distinct from neck, body cylindrical, head dorsolaterally compressed. Rostral pentagonal, about as broad as tall; nasal scales divided, nasal groove contacts the first labial and internasal; internasal scale divided and makes narrow contact with loreal; prefrontal scales slightly smaller than nasals; frontal small, about the same size as the prefrontals, length less than the supraocular scale. Ocular ring consists of one supraocular, one preocular, two suboculars, and two postoculars on the left, one on the right. Loreal single, in contact with upper labials 1 – 4 (third upper labial on the left crowded out by the others and does not touch the loreal). Upper labials 10 / 11, ninth horizontally divided, 5 – 7 contact the suboculars. Lower labials 13, with 1 – 4 contacting anterior chin shield. Three pairs of chin shields, first pair is the largest, third pair smallest and barely distinguishable from the gulars. Dorsal scales keeled and striated; first dorsal row lacks keels; rows on anterior body 25, rows at midbody 23, rows at posterior body 17. Ventrals 147, rounded; subcaudals divided 44 / 45, tail

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

description

Variation. The largest male measured had a total length of 665 mm, with a 117 mm tail. The largest female measured had a total length (TL) of 737 mm, and a 106 mm tail. Scales in the occipital region of the head and on the neck lack keels. Keels are present on most dorsal rows, except the first one (some individuals may also lack keels, or have very weak keels on scale rows 2 through 4). The loreal is usually single, rarely double; usually not in contact with the subocular (75 %). Most (82 %) specimens have the preocular scale in contact with the upper labials 3 - 5; however, the preocular scale did not contact the upper labials in all (n = 3) of the specimens from the Edward River, Queensland population we examined (this same population also showed a horizontally divided postocular). These character states were also seen in specimens from other populations. Upper labials 2 – 4 contact the loreal; the upper labial under the orbit of the eye (and subocular scales) is usually 5 (64 %), or 5 – 6 (25 %), rarely are they 4, 4 + 5, or 6. The posterior upper labials are horizontally divided; the first divided upper labial ranged from 5 to 8, with 7 (54 %) and 8 (39 %) being the most frequ

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

diagnosis

Diagnosis. Cerberus australis can be distinguished from all other members of the genus by its 23 scales rows (range 21 – 25) at midbody, imbricate scales on the crown, lack of keeled scales on crown anterior to the angle of the jaw; lack of contact between first labial and loreal; horizontally divided last upper labial; and mottled venter Cerberus dunsoni has 23 scale rows at mid body, the first labial usually contacts the loreal; and the crown has rounded juxtaposed scales, the venter is a uniform black. Cerberus microlepis has 27 – 31 scale rows at mid-body. Cerberus rynchops has 25 scale rows at mid body (rarely 23); keeled scales on the crown anterior to the angle of the jaw, and the last two upper labials are horizontally divided. Cerberus schneiderii usually has 23 scale rows at mid-body (rarely 21 or 25), the first upper labial usually contacts the loreal.

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

diagnosis

Diagnosis. Cerberus dunsoni can be distinguished from all other members of the genus with 23 scales rows at midbody by its rounded, juxtaposed, plate-like scales on the crown; these scales appear to be thickened compared to the scales of other Cerberus species. The 9 th upper labial is horizontally divided. These characters, combined with large parietal scale fragments and its uniform black venter, make this a very distinctive species. The large, plate-like fragments of the parietals may fuse with the temporal scales. The parietal scales in other Cerberus are usually fragmented into small scales similar to other scales on the crown. The scales on the crown anterior to the level of the angle of the jaw usually lack keels; all other Cerberus with the exception of C. australis have scales with keels anterior to the level of the angle of the jaw. Crown scales are distinctly rounded and juxtaposed; in other Cerberus these scales tend to be sharp-edged and slightly imbricate. Light pigment forms an irregular ventrolateral stripe involving scale rows 1 – 2; this stripe involves rows 1 – 3 or 1 – 4 in other Cerberus with the exception of C. microlepis which has 27 – 29 scale rows at midbod

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species